Cruise Control while on "B"?

You don't mention highway speeds or not. B is same as D except for braking (and regen coasting). At highway speeds the engine is pumping air to help brake. It might keep the ICE on more. Not sure what cruise control does, you'd have to have pretty big hill for it to "foot off pedal"

 

On the Gen 2 and beyond liftbacks, you can't engage (set) cruise control while in B mode.

 

LOL, there must be a reason for it then.. so it does something in extreme hill cases?

 

"B" keeps the engine running even when slowing to a stop and takes some of the energy that regenerative braking can recover. It makes a significant hit in driving and may have been why our first tests with a new Prius in 2001 were so disappointing. In 2001, we rented a Prius for several days but decided to buy an Echo when the Prius MPG did not meet our expectations; the price too high; it had no cruise control; and we could not get one without the navigation unit. Our used, 2003 Prius solved all of these problems and we've been very happy with it. At the time, I found my wife had been driving in "B" (the shifter was new to her) so I speculated that it might have led to her low MPG but there were too many other issues with that car.

The real use of "B" is when descending large hills. We have a 525ft (160m), 8% grade, divided highway that goes up Brindley Mountain which I use for Prius performance testing. What I found is the traction battery significantly warms if descending in "D", 2-3C. But in "B", the traction battery temperature barely moved, 1C. On a trip through hill and mountain country, this can lead to a battery related turtle.

The first reports I remember of battery 'turtle' alarms and slow performance were of folks driving in hilly and mountain areas. Patrick Wong once mentioned a trip to Yosemity where the battery heating required a pause for it to cool down. This was before we realized the risks higher temperatures posed for the original, NiMH battery modules.

Bob Wilson

 

I find cruise control + B to be a really convenient combination when driving through the Appalachians. Most cars (and Prius in D) have cruise controls that can only accelerate you or coast. On a descent you end up still gaining speed anyway. In CC+B you have a cruise that can accelerate, coast, or resist, and accurately maintains your speed on up- and downgrades. It is spookily like having somebody manage accelerator and downshifting for you, and leaves you free to manage steering and watch for the posted speeds of upcoming switchbacks.

Purists will say for the best mileage you don't want your speed accurately maintained up and down, but should emulate large trucks with a more constant power output. Sure, but when you don't feel like doing that, it's really nice that the car can drive itself so well. My passenger thought it was way cool. And I still don't mind the mileage I get on those trips.

Very sorry to hear the feature was disabled in later models. I'll just have to keep my G1 running forever.

-Chap

 

I just got back from a trip to Massachusetts in my C, and I used cruise control (in D) on the Merritt Parkway in Connecticut, which has some good hills. I'm pretty sure that the cruise control also maintained the set speed going downhill, without my having to apply the brakes.

No way to test it here on flat Long Island, but I'll check again on my next trip to the hills.

 

The Gen 3 Prius (and v) do use regeneration aggressively to maintain constant speed downhill when on CC.

 

The best way to answer this question is to test it:

• survey a 10+ mile test route - using any of the popular mapping interfaces, map at least a 10 mile loop that has the types of terrain and speeds you want to test both "CC+D" and "CC+B":
  • minimal traffic or multiple lanes to minimize the risk of external changes
  • stable temperature and minimum wind, 1:00-3:00 AM works great but mid-day works too
  • 0.1-0.2 mile entrance to set drive conditions including speed
• set either "CC+B" or "CC+D" and enter test route - reset trip meter
• read out trip meter at same end-point of route

Then share your results including the test conditions. If your data is interesting, others may choose to replicate the protocol and share their results. In effect, this is how we learn what works. For example, I might choose a route South of the Tennessee River headed either East or West as these would be crossing the maximum number of ridges.

The roads on that side of the river are two-lane roads so I would test after midnight to minimize traffic effects. To avoid altitude changes, there would be four passes, two each direction in either "CC+B" or "CC+D". But I would only use 10+ mile segments with 0.1-0.2 mile 'entrance' and 'exit' runs. Record the data from all four passes and it is done.

Bob Wilson

 

The Gen3 cruise control does apply extra regenerative braking during descents to hold speed down to the set speed. I make considerable use of this feature, which is more efficient than B mode when the traction battery is not filled.

 

I guess it wouldn't surprise me if they integrated the CC better into the HV functions in later generations. In the Classic it really seems to be an off-the-shelf control that may be built into the HV ECU unit but only interacts with it by pulling and pushing the virtual go pedal the way it would have 50 years ago. When speed gets too high the most it can do is let off the go, and that'd be why B helps in the Classic, just because B increases the default resistance applied when the go pedal is let all the way off.

I'm sure there are lots of opportunities to improve efficiency by really integrating the CC with the HV control, which they've probably done in later models, and that way they really could make it maintain speed uphill and down without having to resort to B.

Cool ... I'm glad that ability didn't go away, it just became more seamless.

-Chap

 

I thought the "B" = Brake, and would be good when you down a hill, like 1 and 2 in other automatic cars.

On my way back from Ringwood, NJ, there are hills that making you hit the brakes a lot so I use the B, and it makes me press the brake pedal less.

 

Actually B stands for Brake, nothing is designed to break in B.

 

Sorry I meant Brake

 

I know those hills - I used to have friends in Wanaque, and you definitely need engine braking around there.

I haven't driven my Prius in the area, though; I still had a stickshift BMW the last time I was out there.

 

lol, There is nothing like stick shift for braking and slowing down.